E. histolytica is a cytopathic enteric protozoan that infects nearly 10% of the world's population. Invasion of the colonic epithelium manifests as colitis or liver abscess resulting in an estimated 40-110 thousand deaths annually. Currently no protective vaccine is available. Adherence to the colonic mucosa is an important first step in the pathogenesis of colitis. The 170 kDa subunit of the galactose lectin which mediates adherence to colonic mucins in vitro, has been cloned and appears to be encoded by a gene family. The goals of this proposal are; to determine the copy number and linkage of the members of the 170 kDa gene family, to identify the adherence-inhibitory and enhancing domains of the 170 kDa subunit, and to evaluate the immunoprotective potential of recombinant 170 kDa subunit in an animal model of amebiasis. The molecular organization and copy number of the genes encoding the 170 kDa subunit will first be characterized in order to understand the complexity of the lectin gene family. To identify adherence domains, DNA clones encoding specific portions of the 170 kDa will be expressed individually in E. coli, purified, and used to raise antibody. The region-specific antisera will be tested for the ability to block or enhance amebic adherence to target cells and thus identify the regions of the protein involved in this activity. The amebic liver abscess model developed in the gerbil will be used to evaluate the immunoprotective potential of recombinant 170 kDa subunit. Gerbils will be immunized with the complete subunit or portions thereof. The anti-170 kDa antibody titer and antigen-specific response of immune T cells will be measured. The gerbils will then be challenged intrahepatically with amebic trophozoites and protection against challenge will be analyzed by inspecting the liver for abscesses. The characterization of the 170 kDa subunit of the galactose lectin will be important for understanding the adherence mechanisms of E. histolytica and will assist in the design of protective vaccine against amebiasis which could eventually lead to the prevention of disease and would reduce the global suffering caused by this parasite.